The present invention relates to a phase regulation circuit, in particular for horizontal phase regulation in data displays.
As is known, in the field of displays of data fed by computers, the synchronism signals, both vertical and horizontal, originate from computers of different types, for which there are no unified norms as to duration and phase of the synchronism signals with respect to the video signal.
Accordingly, it is necessary to provide devices capable of rendering a specific data display compatible with the different types of computer. In particular, a regulation device of this kind must allow to recover the phase difference between the active front of the synchronism signal and the video signal in order to obtain the frame picture exactly centered on the screen of the data display. In particular, this phase difference has both a dynamic component, due to the behavior of the drive elements of the data display, and a static component to recover a fixed phase difference between the synchronism signals and the video signal.
Regulation devices are already known, interposed between the computer and the data display, capable of partially compensating this phase difference. In particular, a known phase regulation device comprises a phase-lock stage receiving a reference signal and the snychronism signal generated by the computer and capable of generating a triangular (saw-tooth) wave which, in the steady state, is synchronized with the external synchronism signal. The circuit furthermore comprises a horizontal pulse shaping block receiving the triangular waveform and capable of supplying at the output a series of rectangular pulses supplied to the row drive system of the display. This drive system, typically comprising a transistor, in turn generates a voltage which, suitably squared, is supplied to a phase comparator also receiving the triangular signal generated by the phase-lock stage and a second reference voltage, so as to compensate any phase shift caused by the drive system itself. For this purpose, the phase comparator generates an output signal fed to the square-wave generator so as to anticipate the pulse generated by the latter. Furthermore, to recover any static phase difference between the synchronism supplied by the computer on the video signal, a potentiometer system is provided, acting on the rectangular waveform generator and capable of varying the reference voltages of the latter so as to anticipate or delay the output pulse with respect to the synchronism signal. The more detailed circuit diagram of the known system is illustrated by way of example in FIG. 1.
This known device, though currently in widespread use, is not however free from disadvantages, due to the impossibility of recovering the existing phase difference when the latter exceeds certain levels. In particular, in practice it becomes impossible to recover phase differences greater than approximately one eighth of the period of the processed signal.